Multiple target separator

ABSTRACT

A system for separating and identifying multiple targets within a PPI positioned gate area on a Radar IFF display. The IFF target separator acts upon the IFF response times within the gate and separates the targets in range order regardless of the order of arrival times of the target responses. The targets on the PPI can thus be associated with their respective IFF code readouts.

United States Patent 25 (FROM SYSTEM CONTROL CIRCUITS Fluhr 51 June 20,1972 54'] MULTIPLE TARGET SEPARATOR 3,228,793 6/l967 McLaughlin et al...'.343/s EM [721 manor: Frederick R. mum, Oxon Hill Md. 3,298,0211/1967 Jacobs et al ...343/5 EM [731 Assignee: The United States ofAmerica as Primary Examiner-Benjamin A. Borchelt 'ep fl l y AssistantExaminer-Gregory E. Montone [22] Filed: Aug 27, I970 Attorney-R. S.Sciascia, Arthur L. Branning, J. G. Murray and S. Sheinbein [2]] Appl.No.: 67,328

[57] ABSTRACT 3|. ..343/6.5 R, 3311/5955; A system f e aratin andidentifying multiple targets within n s a PPl positioned gate area on aRadar lFF display. The [F F tar- [58] Field of Search ..343/6.5 R, 6 R,EM, 5 PC get separator acts upon the FF response times wihin the gateand separates the targets in range order regardless of the order [56]Refmnm Cited of arrival times of the target responses. The targets onthe PP] UNITED STATES PATENTS can thus be associated with theirrespective IFF code readouts. 3,312,970 4/1967 Bond ..343/6.5 R3,331,068 7/1967 Busignies ..343/6.5 R 7 China, 2 Drawing Figures 22 A23 Alfva fl zi L swEEP SWEEP (RANGE VOLTAGES) I i'a'i GENERATOR AllflfifT- RANGE m1 our RAEQFHEAIT 3 1 2/ 1 3a 39 L 2 UM. L G: cons r-O FOLLOWNM flTROL mcurrs FLIP mo COMPARATOR mumvnannoa -f" FLOP new il'lfvlli" 1,34 .MST TRIGGER READWTS) mmalr GATE RANGE me our as 37 40 11 FL IP H"1%" COMPARATOR uuunvlaRAroR BD-I PULSE R 7 ggi niai 32 l 45 I ISTTRIGGER -0 GATE A GATE. p INHIBIT RANGE No.3 our 1,3/ 1 ,46 ,38 I 4/ n44 n p a 5 FOLLOW No.3 24 1+ 51-6; 1% Q COMPARATOR luumvsaanon fi 'h Agmu'm l ST TRIGGER P'A'TE'NTEnJuuzo I972 wamm m m0z m TE INVENTOR.FREDERICK R FLUHR LI AGENT M TTORNEY MULTIPLE TARGET SEPARATOR STATEMENTOF GOVERNMENT INTEREST BACKGROUND OF THE INVENTION The present inventionrelates to an IFF active readout control and display and moreparticularly to a PPI type system wherein maximum use is made of targetIF F replies in any one of several modes to furnish a numerical andcoordinate position display of the target identified.

There are many security sensitive areas where air traffic must not onlybe controlled in the conventional sense, which is in itself a highlycomplex problem, but must also be completely identified. Identificationis usually accomplished by some form of IFF (Identification Friend orFoe) where the surface station transmits an interrogating signal whichenergizes a transponder on friendly aircraft to transmit a coded signalthat includes the identity of the aircraft and often its altitude. Theprocessing of the IFF response signals at the surface station is a mostcritical problem for the air controller, particularly when the volume ofair trafiic is large. Because of the excessive time required todetermine the identity of each aircraft, the prior IFF reply display andprocessing system have generally been regarded as inadequate.

It is frequently desirable to track and record for future reference thepositions of a plurality of airborne objects relative to a predeterminedpoint on the ground. Obviously this could be done by employing aplurality of tracking radars, one for each object, each radarcontinuously tracking and providing azimuth, elevation and range datafor its particular object. However, such an arrangement becomesprohibitively expensive where more than a relatively few objects are tobe tracked. Moreover, the problem of designing the individual radar unitso that it will track only its one particular object, despite thepresence of several other similar objects in the same general area, isextremely difficult and makes such a system impractical.

In IFF/Radar display and processing system, there is a continuing needfor separating and identifying multiple targets within a PPI positionedgate area. In IFF, if several targets are in theposition gate area (thegate area positioned over the targets of interest or area on the planposition indicator, PPI), the displayed and decoded IFF codes cannot bereliably associated with the respective targets in the gated area.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide an improved IFF reply display and processing system whereinunambiguous processing of the IFF/Radar data occurring within a PP!position gate area can be made even if multiple targets are locatedwithin this gate area. This is accomplished by a system which includes aradar plan position indicator (PP!) and a light pencil(or any otherstandard gate position control method such as joy stick etc.) controlledby the operator selecting the gated area. Logic circuitry is disclosedwhich permits multiple target separation by storing the ranges of thetargets within the gated area irrespective of the order in which theywere detected and then displaying the SIF (Selective IdentificationFeature) codes on a readout display in the correct range order.

OBJECTS OF THE INVENTION It is therefore an object of the presentinvention to provide an improved IFF reply display and processingsystem.

A further object of the present invention is to provide an improved IFFsystem wherein maximum use is made of the IFF target replies.

Another object of the present invention is to increase the reliabilityof IFF identification.

Yet another object of the present invention is to provide unambiguousprocessing of IFF data occurring within a PP] position gate area.

A still further object of the present invention is to provide separationof multiple targets within a PPI positioned gate area.

Further objects of the invention will become apparent'from the followingdescription and claims especially when considered in conjunction withthe drawings wherein:

DESCRIPTION OF THE DRAWING FIG. 1 shows part of a picture displayed onthe screen of a plan position indicator.

FIG. 2 is a block diagram illustrating the general principles of theinvention.

DESCRIPTION OF THE THE PREFERRE EMBODIMENT Referring now to FIG. 1,during PPI sweep 0, target A would provide a response. On sweep 2,targets A and C would respond in range sequence. On sweep 4, all threetargets A, B and C would respond in order of range, target B respondingearlier in range sequence than target C. The problem is to sort theseradar responses and keep them in proper order so that IFF processingsystems which require two or more IF F responses for proper decodingwill not mix target responses from more than one target.

For situations which would require it, the apparatus shown in FIG. 2allows for the handling of several simultaneous Identity Readoutsoperating from a single PPI gate action and maintains the association ofthe target on the PH and the readout display. The multiple targetseparator maintains the order in range regardless of which target issensed first in time by the operator gating action. A possible situationas illustrated in FIG. 1 will be used to explain the operation of theapparatus shown in FIG. 2.

In FIG. 2, the radar IFF trigger at input 21 initiates sweep generator22 to develop a range sweep voltage at the pulse repetition frequency ofthe radar. Since FIG. 2 is illustrating a three-target capability (whichcan be as many as desired), the sweep generator drives the threefollow-and-hold circuits, 35, 37 and 38. The range sweep generator 22also drives the sweep advance amplifier 23. This amplifier can perfonntwo functions depending on the type of operation desired. The rangesweep can be put on a controlled pedestal in order to advance thesubsequent range gates a fixed range increment prior to the target beinggated. This compensates for the various cumulative delays which canoccur in the system. Also the sweep advance amplifier 23 can be set toincrease the range sweep slope, and provide a percentage of rangeincrease for the early range increment, thus accomodating radar systemrange errors. Either or both of these functions can be provideddepending on operational conditions. The output of the sweep advanceamplifier drives the inputs to the three comparators, 39, 40, 41. Thefollow-and-hold circuits 35, 37, 38 drive the other inputs to thecomparators 39, 40 and 41. The comparators 39, 40, 41 drive the rangegate multivibrators 42, 43, 44 whose outputs are used by the systemcontrol to turn on the proper readout indicators (not shown).

Since the PP! display 25 usually has a high volume of targets displayed,it is necessary for the operator to quickly select a target or area forIFF evaluation. Many suitable devices have been developed for thispurpose, one being a light pencil" gate control in US. Pat. No.3,328,793 issued to Donald J. McLaughlin and Frederick R. Fluhr. While afuller description is available in the referred to patent, the readerwill find the following description of the light pencil 24 gate controlsufficient for the purpose of comprehending the disclosure of thepresent invention.

The light pencil 24 consists of two separated fiber optic bundles incoaxial arrangement. The first outer annular shaped bundle allows alight to be directed onto the PPI 25 so as to select target video foridentification. The inner bundle transmits the light flashes from theselected target video to the detection and processing circuits to gatein the SIP (Selective Identification Feature) code corresponding to theselected target. Thus, the light pencil 24 allows the operator topinpoint a target which he wishes to identify. SIF information codeconsists of a series of one-zero conditions and the exact number of bitpositions can vary according to the particular system and the volume ofinformation to be contained therein. This signal is fed to the numericalreadout lamps (not shown). When the operator places the light detectorportion of the light pencil 24 over the PP] target to be identified, thelight flashes from the PP] 25 are detected and converted to electricalpulses which set flip-flop 3].

In operation, when the PP] position gate (on the order of nmi 10 ispositioned over an area that may contain several IFF targets, the firstlight pulse from the light probe sets flipfiop 31, thus enabling gate32. The first target bracket decode pulse BD-l representing an lFFreply, sets flip-flop 33 which in turn enables gate 34 and sets thefollow-and-hold 35 into the hold" state, thus deriving target range. Ifthere is a second BD-l pulse present (indicating a second target) beforethe maximum range gate in the systems control, flip-fiop 36 is set. Thisaction derives and holds the range of the second target infollow-and-hold 37. This action will continue if a third target ispresent before the end of the system control maximum range gate. Thetarget separator as illustrated will handle three targets separated inrange on a single sweep or on any subsequent sweep within the azimuthgating period. The range values held by the follow-and-hold circuits arecompared with subsequent range sweeps and provide the individual targetrange gate periods. The output of the comparator circuit 39, besidestriggering range multivibrator 42, provides an inhibit pulse to gates 34and 45. Thus, follow-andhold circuits 37 and 38 will not act on therange value held by follow-and-hold 38. Comparator 40 inhibitsfollow-and-hold 38 in a similar manner so that it will not act on thevalue going into follow-and-hold 35. After all three follow-and-holdcircuits acquire range values, the inhibit pulses are not longerrequired.

An example of the operation of the multiple target separator isillustrated by the possible situation of three targets within the PHgate as shown in FIG. 1. When the operator aims his light probe 24 atthe target area to be gated, the first light pulse is generated bytarget A on sweep O. This light pulse sets flip-flop 31 and thus enablesgate 32. When the target A BD-l pulse, passes through gate 32, it setsflip-flop 33. Flop-flop 33 sets follow-and-hold 35 to the hold" stateand thus derives target A range. The setting of flip-flop 33 alsotriggers multivibrator 42, thus deriving the range gate for target A.Since there are no other targets following target A on sweep O, thesystem control maximum range gate operates as indicated in F IG. 1. Onthe next range weep, the target A comparator 39 pulse triggersmultivibrator 42, thus providing the target A range gate. Comparator 39also inhibits gate 34 and gate 45 at target A range only so that targetA will not be stored in follow-and-hold circuits 37 and 38. Again thereare no other targets on range sweep 1 within the system control maximumgate. On the next sweep, sweep 2, the action of target A is repeatedexcept that the BD-l pulse of target C passes through gate 34 and setsflip-flop 36. This triggers multivibrator 43 and sets follow-and-hold 37to hold" thus deriving target C range and providing its range gate. Thisaction repeats until target B is acquired by follow-and-hold 38.

Multivibrators 42, 43, 44 could be turned off by command before theycomplete their range gate period. The sequence in which the circuitsoperate is determined by the sequence of enable signals, and the rangesstored by each circuit can be any of the range of values presented bythe PP! position gate. When the position gate period is ended, thesystem is cleared by a pulse on lead 47 to reset flip-flops 33, 36 and46. The responding target whose SIF code is being displayed isidentified on the PM by a video mark following the target the instantthe final decision is made.

The technique descnbed above allows unambiguous processing of thelFF/Radar data occurring within a PM position gate area. The techniquereceives the responses in any time sequence either/and range and azimuthand provides the correct range gating so that later signal and displayprocessing will not mix target responses and provide an unambiguouscorrelation between the PP] target and its associated SlF code. Thistechnique can be implemented by digital techniques as well as by ananalog method outlined above. While the technique described uses anoperator held light probe to perform the PPI target gating, any otherpositioning method will work just as well, through the light proberequires no modification to the PPI.

Obviously many modifications and variations are possible in light of theabove teachings. It is therefore to be understood that within the scopeof the appended claims the invention may be practiced otherwise than asspecifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. An IFF processing system for separation of multiple radar targets ona plan position indicator and associating each target with its lFF replycomprising:

means for selecting a gated area on said plan position area;

bistable means coupled to said selecting means, said selecting meanssetting said bistable means upon detection of a target within said gatedarea means;

a follow and hold circuit coupled to said bistable means;

means for driving said follow and hold circuits;

whereby said bistable means transmits a pulse to said follow and holdcircuit upon being set, thereby holding the range of said detectedtarget.

2. An IFF system as recited in claim 1, wherein:

said driving means is a sweep generator developing a range sweep voltageat the pulse repetition frequency of the radar; and

a sweep advance amplifier coupled to said sweep generator for advancingsaid gated area.

3. An IFF system as recited in claim 2, including:

a plurality of bistable means;

a plurality of follow and hold circuits coupled to said plurality ofbistable means for storing the range of a plurality of targets withinsaid gated area.

4. An lFF system as recited in claim 3, including comparator meanscoupled to said follow and hold circuits and said sweep advanceamplifier for comparing two consecutive ranges, said comparator outputsinhibiting ensuing follow and hold circuits from storing the same range.

5. An IFF system as recited in claim 4, including multivibrator meanscoupled to said comparator means for supplying a range gate signal tothe IFF readout upon receiving a signal from said comparator means.

6. An IF F system as recited in claim 5, wherein: said selecting meansis a light pencil.

7. An IFF system as recited in claim 6, including means for resettingsaid bistable means after said gated area period is ended.

t k i

1. An IFF processing system for separation of multiple radar targets ona plan position indicator and associating each target with its IFF replycomprising: means for selecting a gated area on said plan position area;bistable means coupled to said selecting means, said selecting meanssetting said bistable means upon detection of a target within said gatedarea means; a follow and hold circuit coupled to said bistable means;means for driving said follow and hold circuits; whereby said bistablemeans transmits a pulse to said follow and hold circuit upon being set,thereby holding the range of said detected target.
 2. An IFF system asrecited in claim 1, wherein: said driving means is a sweep generatordeveloping a range sweep voltage at the pulse repetition frequency ofthe radar; and a sweep advance amplifier coupled to said sweep generatorfor advancing said gated area.
 3. An IFF system as recited in claim 2,including: a plurality of bistable means; a plurality of follow and holdcircuits coupled to said plurality of bistable means for storing therange of a plurality of targets within said gated area.
 4. An IFF systemas recited in claim 3, including comparator means coupled to said followand hold circuits and said sweep advance amplifier for comparing twoconsecutive ranges, said comparator outputs inhibiting ensuing followand hold circuits from storing the same range.
 5. An IFF system asrecited in claim 4, incluDing multivibrator means coupled to saidcomparator means for supplying a range gate signal to the IFF readoutupon receiving a signal from said comparator means.
 6. An IFF system asrecited in claim 5, wherein: said selecting means is a light pencil. 7.An IFF system as recited in claim 6, including means for resetting saidbistable means after said gated area period is ended.